A welding controller for controlling welding operation in accordance with welding condition data as stored in a memory as shown in FIG. 3 has been conventionally commonly known.
That is, in FIG. 3, a CPU 21 controls a welding machine in accordance with a system program stored in a ROM 22. A fixed program, fixed data and the like for controlling welding operation (hereinafter referred to as welding control fixed program and fixed data) are stored in the ROM 22, and operation instruction and the like are stored in a RAM 23. The CPU 21 controls welding operation upon reading the welding control fixed program, fixed data, operation instruction and the like from the ROM 22 and the RAM 23.
Data such as change of welding condition and the like during welding operation is written into the RAM 23, and the welding operation is carried out under the changed condition. Upon completion of the welding operation, welding control data is stored in the RAM 23 and it is read from the RAM 23 at the start of the next welding operation.
The RAM 23 is connected to a control power supply 24 and also connected to a battery 26 via the control power supply 24 and a changeover switch 25, wherein the welding control data stored in the RAM 23 is held by a power supply from the battery 26 when the control power supply 24 is turned off, thereby protecting the welding control data. The changeover switch 25 for turning off the control power supply 24 is operated upon reception of a signal from a voltage detection circuit 27 for detecting a value of the power supply inside the welding controller at the time when the power supply inside the welding controller is lower than a prescribed value.
However, the conventional well known welding controller has the following drawbacks. That is, firstly, if information stored in the RAM is held by an auxiliary power supply such as the battery 26 and the like, information to be stored cannot be held in the RAM when a cell of the auxiliary power supply is consumed or it is deteriorated with lapse of time, i.e., subjected to aged deterioration, thereby braking data. Secondly, even if the cell of the auxiliary power supply is neither consumed nor subjected to aged deterioration when thereof occurs a loose connection at the junction between the battery inclination face 26 and the changeover switch 25, information can not be held in the RAM, thereby braking data. Thirdly, if the CPU 21 is erroneously operated for some reason, the CPU 21 effects unexpected operation so that abnormal data is written into the RAM 23, thereby braking data. Fourthly, since the battery 26 or a capacitor having high capacitance is used, a period for holding data becomes finite.